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An Investigation into the Al-6wt%Mg work Hardening Behavior after Cold Rolling

Abdollahzadeh, Amin | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 48527 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Kazeminezhad, Mohsen
  7. Abstract:
  8. Al-6wt%Mg alloy has been enormously exploited in aerospace industry. Since for production of this alloy in the form of sheets of different thickness, the cold rolling process is used, thus to understand the final mechanical properties of the rolled alloy products, their work hardening should be examined. Also, one of the important phenomena that occurs in cold state of the alloy is dynamic strain-aging (DSA), which can cause serrations in realistic stress-strain curve. The aforementioned issue is discussed in the current study. Therefore, the work-hardening values for the mentioned alloy during and after rolling is determined, and then compared with the experimental studies. The results of this study showed that by increasing both the rolling strain (R%) and rolling speed, length of serrated area decreased. Also increase of rolling strain significantly enhanced the strength values; the ultimate strength value illustrated an increase from annealed state (318 MPa) to 70% strain state (480 MPa). However, the effect of rolling speed was insignificant, i.e. through an increase in rolling speed in 15% strain, the strength showed a raise from 336 MPa to 348 MPa. This increased strength reduced work-hardening that also included an intense fall in strain-hardening rate. Regarding the Al-Mg alloys containing a high percentage of magnesium, the initial plastic flow occurred at high work-hardening rate. This behavior was in response to the second stage of work-hardening in polycrystals, which was rapidly followed by the third stage of the work-hardening; so that the work-hardening rate decreased linearly in regard to the flow stress.Grains in the microstructure of the alloy became finer and longer by increasing both the amounts of rolling strain and strain rate. By increasing the amount of rolling strain and strain rate, the distribution percentage of secondary phase precipitates increased, so that distribution percentage rose from 21.1% in non-rolled condition to 72.2% in the condition of strain 70% and the rolling speed 50 rpm. In this circumstance, the size of the precipitates decreased; from 82.6 μm in non-rolled condition to 38.3 μm in the condition of strain 70% and the rolling speed 50 rpm. Furthermore, a uniform distribution of the precipitates was obtained, which was attributed to the reduced work-hardening rate (the latter due to the increased flow stress)
  9. Keywords:
  10. Work Hardening ; Aluminum-Magnesium Alloy ; Cold Rolling ; Dynamic Strain Aging

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